Anatomic vertebral cage

ABSTRACT

A spinal fusion system includes a cage with a fillable volume and removable locking gate, thereby enabling the fillable volume to be packed with graft, biologic or other materials prior to the gate being closed and locked. In the preferred embodiment, the locking gate is positioned anteriorally, though lateral, posterior, and combinations thereof are also possible. The cage is preferably radiolucent, being composed of a carbon fiber, but with one or more radiopaque markers to provide a certain degree of visualization. Some or all of the walls of the cage may include superior and/or inferior surface features to enhance positioning and/or minimize back-out, and the posterior wall may be indented to prevent neurocompression. The sidewalls of the cage may further include a recessed face with nipple indents and locking fasteners. According to a system aspect of the invention, multiple cages are provided, each being shaped differently for use at different spinal levels. For example, the cage may be larger and more trapezoidally-pronounced for the L5-S1 levels, or smaller and less trapezoidally pronounced for the T and L2 levels. The system may further including an implant introducer instrument geometrically matched to the cage, and the matched implant introducer instruments and cages may be color-coded to expedite the procedure.

REFERENCE TO RELATED APPLICATION

[0001] This application claims priority from U.S. Provisional PatentApplication Serial No. 60/388,974, filed Jun. 14, 2002, the entirecontent of which is incorporated herein by reference.

FIELD OF THE INVENTION

[0002] This invention relates generally to spinal fusion and, inparticular, to an anatomic, fillable cage and instrumentation therefore.

BACKGROUND OF THE INVENTION

[0003] There are many surgical approaches and methods used to fuse thespine. Most involve the placement of a bone graft between the vertebrae.Supplemental hardware, such as plates, screws and cages may or may notbe used, depending upon the indication.

[0004] An early cage design is described in U.S. Pat. No. 4,501,269 toBagby, entitled “PROCESS FOR FUSING BONE JOINTS.” According to themethod, a hole is bored transversely across the joint and a slightlylarger cylindrical basket is driven into the hole, thereby spreading thebones in resistance to the tensile forces of the surrounding tissue.Immediate stabilization of the joint is achieved by the implantation ofthe rigid cylindrical basket. Subsequent bone-to-bone fusion isachieved, both through and about the basket, which is filled with bonefragments produced during the boring step.

[0005] The Bagby patent states that the process is applicable to anyhuman or animal joint formed by opposed contiguous bony surfaces whichare covered and separated by intervening cartilage and are surrounded byligaments which resist expansion of the joint. Specific examples of suchjoints are a spinal joint between adjacent vertebrae or the ankle joint.This stand-alone interbody fusion technique continued to evolve withmaterial changes and the design of threaded cages to increase stabilityand decrease displacement rates. Bilateral, parallel implants weredesigned for use in the lumbar spine, with the first human implantationoccurring in the early 1009s. The cylindrical titanium cages werethreaded to screw into the endplates, thereby stabilizing the device andallowing for increased fusion rate with a stand-alone anterior device.

[0006] Ray and colleagues developed a similar titanium interbody fusiondevice which was initially used in posterior lumbar interbody fusions(PLIF), but expanded to include ALIF procedures. In 1985, Otero-Vichreported using threaded bone dowels for anterior cervical arthrodesis,and femoral ring allograft bone has subsequently been fashioned intocylindrical threaded dowels for lumbar application.

[0007] Currently, there are a wide number of available interbody fusiondevices of varying design and material, including:

[0008] 1) Cylindrical threaded titanium interbody cages;

[0009] 2) Cylindrical threaded cortical bone dowels; and

[0010] 3) Vertical interbody rings, boxes and wedges.

[0011] All existing devices are prefabricated and not anatomicallyshaped, thus requiring the intervertebral space to be shaped toaccommodate the device. This requires multiple steps and tools toprepare the area, distract, measure, and trial/size prior to ultimateplacement. The requisite distraction devices and trial sizers interferewith the actual device for implant, creating more steps and decreasingthe accuracy of placement. Other solutions, such as mesh cages and bonematerials, are prone to deformation and/or breakage when attempts aremade to force them into the discal interspace.

[0012] As a consequence of these limitations, only a small area of theendplate surface remains proximate to bone graft, which is dictated bythe size and position of the cage. With current approaches, it is alsodifficult to visualize bone fusion mass because the cages and otherdevices are metal, and large trays are required with many instruments,due to the large number of different sized cages.

SUMMARY OF THE INVENTION

[0013] This invention improves upon existing solutions by providing aspinal fusion system including a cage with a fillable volume andremovable locking gate, thereby enabling the fillable volume to bepacked with graft, biologic or other materials prior to the gate beingclosed and locked. In the preferred embodiment, the locking gate ispositioned anteriorally, though lateral, posterior, and combinationsthereof are also possible.

[0014] The cage is preferably radiolucent, being composed of a carbonfiber, but with one or more radiopaque markers to provide a certaindegree of visualization. Some or all of the walls of the cage mayinclude superior and/or inferior surface features to enhance positioningand/or minimize back-out, and the posterior wall may be indented toprevent neurocompression. The sidewalls of the cage may further includea recessed face with nipple indents and locking fasteners.

[0015] According to a system aspect of the invention, multiple cages areprovided, each being shaped differently for use at different spinallevels. For example, the cage may be larger and moretrapezoidally-pronounced for the L5-S1 levels, or smaller and lesstrapezoidally pronounced for the T and L2 levels. The system may furtherinclude an implant introducer instrument geometrically matched to thecage, and the matched implant introducer instruments and cages may becolor-coded to expedite the procedure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIGS. 1A and 1B illustrate an intervertebral cage according to theinvention including contoured, dome-shaped sidewalls and a flat,trapezoidal under surface;

[0017]FIG. 2 is a drawing which shows this detachable ratchet handle;

[0018]FIG. 3 is a drawing which shows contoured wedge-shaped retractorsaccording to the invention;

[0019]FIG. 4 is provides different views of the U-cage introducer;

[0020]FIG. 5 is a drawing of a graph impactor;

[0021]FIG. 6 shows a gate holder according to the invention;

[0022]FIG. 7 illustrates a screwdriver, attached to the detachableratchet handle;

[0023]FIG. 8A is a top-down view of cage shapes applicable to L2-L5;

[0024]FIG. 8B illustrates larger, preferably more trapezoidally-shapeddevices for L5-S1 levels;

[0025]FIG. 8C shows smaller, less trapezoidal and less dome-shapeddevices applicable to T and L2 levels;

[0026]FIG. 9A illustrates the removal of disc material between the L4and L5 levels;

[0027]FIG. 9B shows dilation;

[0028]FIGS. 9D and 9E depict cage placement;

[0029]FIG. 9E, shown from an oblique perspective, illustrates how theendplates are easily accessed according to the invention.

[0030]FIG. 10A shows how the endplates are prepared and the space ispacked with graph/biologic material, as appropriate; and

[0031]FIG. 10B shows how a correspondingly sized anterior plate islocked in place using the gate holder and locking screws.

DETAILED DESCRIPTION OF THE INVENTION

[0032] This invention improves upon the prior art by providing a cagesystem with significant advantages, independently and in combination.The system is capable of a custom fit while, at the same time,eliminates multiple steps, instruments and trays, and allows easier andgreater access to endplate surface area. The invention can be used withautograph, allograph, and/or biologic materials.

[0033] In the preferred embodiment, the device according to theinvention takes the form of a carbon fiber-faced cage. The structure isgenerally radiolucent, while including small radiopaque markers toprovide some degree of visualization.

[0034] In terms of apparatus, the cage preferably includes contoured,dome-shaped sidewalls with a flat, trapezoidal under surface, as shownin FIGS. 1A and 1B. Separate cages are provided along with tools forlevels L5 to S1, which typically require a more pronounced trapezoidalshape.

[0035] Also in the preferred embodiment, the back wall of the cage isindented to prevent neurocompression. The sidewalls also preferablyinclude a recessed face with nipple indents and locking screw holes. Aclosing face gate with non-slip nipples and locking screw holes areprovided along with fasteners, such as a pair of locking screws.

[0036] Thus, in terms of an intermediate summary, some of the uniquefeatures of this invention include a cage having dome-shaped contoursfor the upper endplate, different shapes for the L5-S1 level, anindented back wall and an open face with a closing gate including alocking mechanism. Since it is considered that many, if not all, ofthese features are independently unique and therefore patentable, thisinvention anticipates any of these features alone or in combination.

[0037] The invention further includes instrumentation, also consideredto represent novel subject matter. A series of contoured, wedge-shapeddistracters are provided, preferably including a color-coded centeringmark. Separate distracters are used for the trapezoidal-shaped L5 to S1levels. A correspondingly coded final “U-cage introducer” is includedalong with ring curettes, claws and endplate prep tools, and the like.Additionally, a graph impactor and gate holder/screwdriver are used,preferably in conjunction with a detachable ratchet handle.

[0038]FIG. 2 is a drawing which shows this detachable ratchet handle.FIG. 3 is a drawing which shows contoured wedge-shaped retractorsaccording to the invention. FIG. 4 is provides different views of theU-cage introducer, and FIG. 5 is a drawing of a graph impactor. FIG. 6shows a gate holder according to the invention, and FIG. 7 illustrates ascrewdriver, attached to the detachable ratchet handle which can be usedwith any of the instruments shown in FIGS. 2-6 as well.

[0039] With respect to the implants, and as discussed elsewhere herein,varying sizes of U-shaped cages are provided, which may includecrescent-shaped sidewalls, domed tops, and indented back walls. Again,these are composed of carbon fiber with radiopaque markers, andpreferably include serrated or tooth-edged endplate surfaces to enhancegripping and to prevent back out. Correspondingly sized anterior gatesare provided, also preferably composed of carbon fiber, having non-slipnipples and holes to receive locking fasteners such as screws. FIG. 8Ais a top-down view of shapes applicable to L2-L5. FIG. 8B illustrateslarger, preferably more trapezoidally-shaped devices for L5/S1, and FIG.8C shows smaller, less trapezoidal and less dome-shaped devicesapplicable to T and L2 levels.

[0040] In terms of surgical protocol, an anterior approach is used toaccess the intervertebral space. Disc material is removed asappropriate, and the lateral extent of the disc space is determined. Thedisc space is then dilated to an appropriate height utilizing thecolor-coded distracters according to the invention. Upon removal of thefinal distracter, it is replaced with the same, color-coded implantintroducer instrument. The implant is released and the introducer toolis removed. FIG. 9A illustrates the removal of disc material between theLA and L5 levels. Dilation is shown as FIG. 9B and cage insertion shownin FIG. 9C. The cage in place is shown in FIGS. 9D and 9E. 9E, shownfrom an oblique perspective, illustrates how the endplates are easilyaccessed according to the invention.

[0041] As shown in FIG. 10A, the endplates are prepared and the space ispacked with graph/biologic material, as appropriate. A correspondinglysized anterior plate is then locked in place using the gate holder andlocking screws and screwdriver, as shown in FIG. 10B. The wound is thenclosed, completing the procedure.

I claim:
 1. A spinal fusion system, comprising: a cage structureincluding a posterior wall and opposing lateral sidewalls defining afillable volume; and a removable locking anterior gate, enabling thefillable volume to be packed with graft, biologic or other materialsprior to the gate being closed and locked.
 2. The spinal fusion systemof claim 1, wherein the cage is substantially radiolucent.
 3. The spinalfusion system of claim 1, wherein the cage is composed of a carbonfiber.
 4. The spinal fusion system of claim 1, wherein the cage issubstantially radiolucent, but further including one or more radiopaquemarkers to provide a certain degree of visualization.
 5. The spinalfusion system of claim 1, wherein some or all of the walls includesuperior and/or inferior surface features to enhance positioning and/orminimize back-out.
 6. The spinal fusion system of claim 1, wherein theposterior wall is indented to prevent neurocompression.
 7. The spinalfusion system of system 1, wherein the sidewalls include a recessed facewith nipple indents and locking fasteners.
 8. The spinal fusion systemof system 1, wherein the cage is shaped differently for use at differentspinal levels.
 9. The spinal fusion system of system 1, wherein the cageis shaped differently for use at different spinal levels.
 10. The spinalfusion system of system 1, wherein the cage is trapezoidally shaped. 11.The spinal fusion system of system 1, wherein the cage is larger andmore trapezoidally-pronounced for L5-S1.
 12. The spinal fusion system ofsystem 1, wherein the cage is smaller and less trapezoidally pronouncedfor the T and L2 levels.
 13. The spinal fusion system of system 1,further including an implant introducer instrument geometrically matchedto the cage.
 14. The spinal fusion system of system 13, wherein thematched implant introducer instruments and cages are color-coded.